Fuels, plastics, and chemicals derived from agricultural feedstocks are receiving considerable attention as the world looks for alternatives to petroleum. Production of polyhydroxyalkanoates (PHAs), a family of naturally renewable and biodegradable plastics, in crops has the potential of providing a renewable source of polymers and bio-energy from one crop if plant residues remaining after polymer isolation are converted to liquid fuels and/or energy. PHAs can provide an additional revenue stream that would make crops including bioenergy crops more economically viable.
PHAs are a natural component of numerous organisms in multiple ecosystems and accumulate in a wide range of bacteria as a granular storage material when the microbes are faced with an unfavorable growth environment, such as a limitation in an essential nutrient (Madison et al., Microbiol. Mol. Biol. Rev. 63:21-53 (1999); Suriyamongkol et al. Biotechnol Adv. 25:148-75 (2007)). The monomer unit composition of these polymers is largely dictated by available carbon source as well as the native biochemical pathways present in the organism. PHAs can be produced industrially from renewable resources in bacterial fermentations providing an alternative to plastics derived from fossil fuels. PHAs possess properties enabling their use in a variety of applications currently served by petroleum-based plastics and are capable of matching or exceeding the performance characteristics of fossil fuel derived plastics with a broad spectrum of properties that can be obtained by varying the monomer composition of homo- and co-polymers, or by manipulating properties such as molecular weight (Sudesh et al., Prog. Polym. Sci. 25:1503-1555 (2000)).